1. Field of the Invention
The present invention relates to a pad dresser, a polishing device, and a pad dressing method, and in particular, to the pad dresser for reproducing a surface of a polishing pad of the polishing device which polishes a work, such as a semiconductor wafer, the polishing device provided with that, and the pad dressing method.
2. Description of the Related Art
As miniaturization of a semiconductor device and multi-layering thereof progress, CMP (Chemical Mechanical Polishing) technology has become an essential technology indispensable to the manufacturing process of the semiconductor device. This CMP technology has been utilized for various processes now, such as not only flattening of an interlayer insulation film but Cu wiring and element isolation.
As one of important specifications in flattening CMP, there is an in-surface uniformity of a work (polishing uniformity) of a removal rate. In order to enhance the polishing uniformity, it becomes important to distribute uniformly factors which influence the removal rate in the in-surface of the work.
While there is polishing pressure, relative velocity of the polishing, etc. as the important factors, there is a surface state of the polishing pad as the important factor of which the quantification has not progressed conventionally. The desirable surface state of the polishing pad is formed with the pad dressing. Therefore, for example, also from the fact that the removal rate abruptly falls when the pad dressing is suspended in so-called an in-Situ dressing in which the pad dressing is simultaneously performed in the midst of polishing, it is also clear that the strict control of the surface state of the polishing pad is important.
The pad dressing means that by making the pad dresser (“dresser” may just be called henceforth) to which grindstones such as a diamond are attached abut the polishing pad, and cutting the surface of the polishing pad or roughening the surface, etc., the retentivity of slurry is made to be good to initialize the pad into a polishable state, and the retentivity of slurry is made to recover for the polishing pad in use, and the polishing capability is made to be maintained.
As the pad dresser, the dresser in which a diamond abrasive grain is electrodeposited is used conventionally, and in many cases, used is the dresser which is made to rotate in the surroundings of an axis and made to be pressed on the polishing pad and performs dressing of the polishing pad (for example, refer to Japanese Patent Laid-Open Publication No. 2001-274122 or Japanese Patent Laid-Open Publication No. 2003-181756).
FIG. 18 is a conceptual diagram for describing the pad dresser described in Japanese Patent Laid-Open Publication No. 2001-274122. As for pad dresser 130 described in Japanese Patent Laid-Open Publication No. 2001-274122, as shown in FIG. 18, substrate 131 on which diamond abrasive grains 133, 133, . . . , are electrodeposited is fixed and attached to support part 132.
FIG. 19 is a conceptual diagram for describing the pad dresser described in Japanese Patent Laid-Open Publication No. 2003-181756. Pad dresser 130A described in Japanese Patent Laid-Open Publication No. 2003-181756, in principle as shown in FIG. 19, is composed so that substrate 131A on which diamond abrasive grains 133, 133, . . . , are electrodeposited is attached swingably in all directions to support part 132A via a so-called gimbaled structure such as ball joint 132a, for example, and follows the surface of polishing pad 20.
What is provided with a brush dresser besides a diamond dresser is known (for example, refer to Japanese Patent Laid-Open Publication No. 2003-211355). The diamond dresser which is a first dresser cutting the polishing pad surface and a second dresser for scraping out the debris stuffed up in a concave portion of the polished surface of the polishing pad are disclosed.
Since the brush dresser makes it the object to scrape out the debris stuffed up in the concave portion of the polished surface, the diamond dresser which is the first dresser bears the dressing with regard to the so-called pad dressing cutting the pad.
A nylon brush is used as a material used in the brush dresser. However, although the nylon brush has an ability to brush the pad surface, the brush has no effect of cutting off the pad surface.
Here, an investigation which ascertains an effect of the pad dressing was performed in advance of the present invention. First, the polishing pad surface is brushed with the nylon brush, supplying pure water without cutting the polishing pad surface, and the recovery of the removal rate in the polishing pad which was made to be clogged was evaluated. However, in spite of prolonged pure-water feed and brushing, the recovery of the removal rate was at most only 31.4%. At this time, SEM observation of the polishing pad surface was performed and it was confirmed that the debris of the polishing pad surface was removed finely. [Related literature: Daichi Kamikawa and Takashi Fujita, et al., the transaction of the symposium in Tohoku Branch Office of the Japan Society for Precision Engineering, p22, 2004]
This experiment has clarified that just only removing the debris staying on the surface of the polishing pad by brushing does not mean having performed the pad dressing. After this experiment, by performing the usual diamond dressing process that cuts the polishing pad surface, the recovery of the removal rate has been confirmed, and it is concluded that there is the need of cutting off the polishing pad surface for performing the pad dressing. In addition, in the case of brushes made of resin, such as nylon, when cutting the pad made from polyurethane which is the same resin material, since it is the same resin material, both sides are similarly worn out and decay, and it is easily understandable for one skilled in the art that cutting the pad will not be realized thereby.
In addition to this, in the removal rate lowering process according to the clogging on the polishing pad, it is also shown clearly that reforming of the surface of the polishing pad is performed chemically. Thus, it is concluded that being reformed chemically like this is also one factor that reduces the removal rate. [Related literature: Takashi Fujita et al., the transaction of the symposium in the spring convention of the Japan Society for Precision Engineering, p 845, 2005]
Therefore, in the pad dressing, because there is the effect according to the reforming of the polishing pad itself, except for the effect of the removal rate reduction caused by the concave stuffed up on the surface of the pad, it can be understood also from such cases that the polishing pad must be cut in order to recover the pad state completely.
From the situations mentioned above, the inventor of the present invention has clarified that the effect of scraping out the debris of the polishing pad surface is insufficient as the dressing for maintaining the removal rate, and cutting off the reformed pad surface is indispensable.
The pad dressing is often used mixing with the pad brushing. However, in consideration of such cases, the pad dressing is defined here as follows as contrasted with the pad brushing. The pad dressing is made to be defined as the process which keeps the pad state uniform by roughening the surface with cutting the pad physically. On the other hand, the pad brushing is made to be defined as the process for removing, without cutting, grinding waste etc. which are included in the concave of the pad. Both are clearly distinguished even in the functional aspect by whether cutting off and removing physically the reformed pad surface itself or not.
Therefore, in the disclosed technologies, there is no content of performing the dressing in which the pad surface is cut off with the brush, and they are used consistently as the means for removing debris which are staying on the pad surface.
In addition, disclosed is the technology which describes the dressing using a brush (for example, refer to Japanese Patent Laid-Open Publication No. 2003-181756 or Japanese Patent Laid-Open Publication No. 10-329003). However, the brush dressers given in Japanese Patent Laid-Open Publication No. 2003-181756 and Japanese Patent Laid-Open Publication No. 10-329003 as well as in Japanese Patent Laid-Open Publication No. 2003-211355 are descriptions as the brushing method for scraping out the debris on the polishing pad, and are not the dressing for cutting off the surface of the polishing pad.
As a technology describing the dressing using the brush, the configuration which uses comparatively high rigidity materials, such as a metal wire, is shown as a polishing adjusting element (here, dresser) in order to give a texture to a polishing web (Japanese PCT National Publication No. 2002-515833).
However, in Japanese PCT National Publication No. 2002-515833, the polishing web is pulled and adjusted with a rolling turn bar, and the pad surface is adjusted against the polishing web stretched. In such a case, the dressing on the reference of the fixed-supported pad surface is not performed. It is because the pressure of the dressing involves various factors, such as the tension of the pad.
As a technology which describes the dressing using a brush similarly, the method in which the surface of the surface-roughening member which is supported by the flexible material performs dressing with following the undulation of the pad and contacting thereto is described. An embodiment which uses a brush as the surface-roughening member is also described (Japanese Patent Laid-Open Publication No. 10-315117).
However, in Japanese Patent Laid-Open Publication No. 10-315117, the portion which fixes the surface-roughening member and the flexible material is attached to an adjustment arm by a pin hinge. That is, even if the brush is used, the point group operates as one surface as a whole. Since the overall brush chamfer cants against the pad surface according to the frictional force received by brush chamfer, the intermittent contact to the pad by the dresser stated previously cannot be avoided as a result. Therefore, the surface reference dressing on the reference of the pad surface is not realizable. From the description that this is compatible with the diamond type as the surface-roughening member, the brush taken up here is only what has the function which performs surface-roughening of the pad to the last, and it can be also understood easily that it is not what has the dressing function on the reference of the pad surface.
A method for performing the dressing of the pad surface in double-sided polishing using a brush is shown (Patent documents 7). However, since it is stated that the hard brush to such an extent of no buckling distortion is used as the configuration of the brush and the method is not what allows elastic deformation of the brush, the method does not make the surface reference dressing possible either.
A brush dresser for eliminating a concave portion of the surface of the polishing pad is shown (Patent documents 8). However, since eliminating the concave portion of the pad surface is described, it is not what performs the dressing along the shape of the pad surface. Since the dresser (FIG. 12) of the brush is described as compatible in terms of parallel as the diamond type dresser (FIG. 10) and the ceramics dresser (FIG. 11), just providing a convex-concave shape on the dresser surface and cutting off the surface of the polishing pad by the dresser having such the surface shape, are considered to be the purpose.
In this, the configuration and the method of performing dressing uniformly on the reference of the pad surface by the elastic deformation of the material are not suggested, and a dressing method which corrects the surface flatly is shown.
Further, as a dressing method with respect to a grinding stone, a dresser which is formed by kneading a super-hard abrasive grain in a nylon brush is shown (Japanese Patent Laid-Open Publication No. 2002-273656).
Since it is the dressing for the grinding process, the hard abrasive grain kneaded into the nylon brush is dropped when performing dressing and the growing wild of the dresser itself is assumed. When used for flattening etc. of a semiconductor wafer stated in this case, if the diamond abrasive grain drops in the case of the dressing, for example, the abrasive grain will be put between the polishing pad and the wafer, and a fatal scratch will be given on the wafer surface. Therefore, the dresser which causes falling of the abrasive grain is excluded from the specifications which are the prerequisite as a dresser for polishing of the semiconductor wafer.
A dressing method which performs a surface reference dressing on the reference of the surface of the polishing pad is shown (Japanese Patent Laid-Open Publication No. 2007-90516).
However, in Japanese Patent Laid-Open Publication No. 2007-90516, if the wire size of the wire rod is made thick in the case of each wire type member operates independently, the rigidity will become large. However, when the wire size is thick, the effective incision depth cannot be given on the pad. Even if the effective incision depth can be given on the pad by excessive force, since the minimum amount with which the pad is cut will become large, the situation where the pad surface is plucked rather than cut and roughened arises.
In a pad dressing, the plucking a pad surface leads to plucking a hydration sphere which includes slurry etc. moderately in the pad surface, and the retentivity of slurry on the pad surface may be made to get worse on the contrary. The hydration sphere holding the slurry, depending also on the material of the pad, is about few-dozens μm order in the case of the foaming polyurethane. Even if cutting off is performed within that, the minimum amount volume of the cutting off where the hydration will continue to be maintained is from several micrometers to about ten micrometers. Therefore, in the case of the dresser which uses the thick wires, it is difficult to roughen the pad with cutting the pad finely.
On the other hand, if each wire rod is made fine, it will be considered possible to roughen the pad finely. However, when each wire rod is made fine, since the bending rigidity of each wire rod becomes small, there is not rigidity of the wire rod to the extent that the effective incision depth is obtained, and it becomes difficult to perform the dressing itself which roughens the pad surface with cutting off thereon.
Even if the dresser has the wire size to the extent that cuts and roughens the pad finely, there is a problem of the abrasion of the tip part next. Although sufficient rigidity to the extent of cutting the pad surface is secured with the wire rod of about 0.25 mm in wire size for example, there is a problem of the abrasion of the tip part. Usually, in the case of that a high hardness material like the diamond is used as the abrasive grain, it is possible for the sharpness at the tip of the abrasive grain to secure a certain amount of processing time, and the capability to cut the pad is stabilized in the time frame. However, it is extremely difficult to attach the diamond abrasive grain at the tip of the fine wire rod like 0.25 mm by electrodeposition etc. Therefore, it is desired to perform dressing by the tip part of the wire rod itself. However, in the case of that the dressing is performed by SUS of a metallic material, etc., for example, since the abrasion resistance is extremely low compared with the diamond etc., the tip part blunts immediately. As a result, the continuation of cutting and roughening of the pad itself became impossible with the blunting, and it was extremely short-lived.
From the above, there has been the problem in which even if a fine wire rod about 0.25 mm of a wire size is used, the time frame which can be used substantially is extremely short by the progress of the blunting of the tip
Further, in the case of that a plurality of element wires are simply bundled together, and the vicinity of the tip part is all constrained like the upper part altogether, there is the problem where the effective amount of incision cannot be given. This is because, although the tip part operates as an individual point, if the tip part exists very densely, the pressure which one tip point extends on the pad abruptly decreases even if the tip point is individual. In an extreme case, in the case of bundling a plurality of element wires in very high density and without any gap therebetween, the tip parts of the element wires are considered to operate as one surface instead of the individual tip point. As the result, it becomes impossible to give effective incision for cutting the pad, and it becomes impossible to perform the pad dressing of roughening the pad with cutting off thereon.
By the way, since a polishing pad used with CMP device has thickness unevenness of the polishing pad itself, and attachment unevenness to the polishing surface plate, the polishing pad surface after the attachment thereon is not planar. The polishing pad surface after the attachment usually has a vertical interval (ups and downs) of an undulation (about 30 μm to 50 μm).
However, in CMP, in order to polish a in-surface of a wafer uniformly, it is required to perform dressing uniformly (following) following the surface of ups and downs also on the polishing pad surface which has such ups and downs.
FIG. 20 is a diagram showing a concept of a specification of a pad dressing required of CMP. As shown in FIG. 20, in the case of performing dressing of the polishing pad 20 in which the undulation is formed in about 100 mm in the width and in about 50 μm in the vertical interval, for example, it is required to perform dressing uniformly with following the undulation. Thus, since the polishing pad is an elastic material, the pad dressing in CMP device can be regarded as a surface reference grinding process of the elastic material.
However, pad dresser 130 described in the above-mentioned Japanese Patent Laid-Open Publication No. 2001-274122, since the dresser (namely, substrate 131 on which diamond abrasive grains 133, 133, . . . , are electrodeposited) is completely fixed to support part 132 as shown in FIG. 18, only the convex portion of the undulation of the polishing pad surface will be cut off. Therefore, there is a problem that the uniform dressing along the polishing pad surface is not performed.
As shown in FIG. 19, although pad dresser 130A described in the above-mentioned Japanese Patent Laid-Open Publication No. 2003-181756 is supported so that the dresser surface may follow the surface of polishing pad 20, in a actual pad dressing, the dresser cannot follow the polishing pad surface, and cannot perform dressing uniformly. It is because the pad dresser cants against the polishing pad 20 since a large frictional force works on the pad dresser surface in contact with polishing pad 20 which is moving in a high speed. Since the pad dresser returns to the original attitude when the friction is reduced with the pad dresser canted, as a result, the pad dresser will contact polishing pad 20 intermittently (stick slip).
Dispersion (ununiformity) in the dressing in the in-surface of such polishing pad 20 causes the following problems against the polishing performance on a wafer. First, since the portion where the dressing is performed in the in-surface of the polishing pad and the portion where the dressing is not performed therein, are intermingled, the polishing unevenness (polishing dispersion) is generated in the in-surface of the wafer. Next, in a process step of starting polishing the pad, since the dressing of the whole surface is not performed uniformly but the dressing area expands gradually, it takes time for the removal rate to be saturated. Since the one whose removal rate is not saturated cannot be used for the product processing, the rise time of the polishing pad becomes long as a result.
Further, in the case of performing dressing of the polishing pad using the traditional diamond electrodeposition plate, the overall pad dresser system will repeat intermittent contact according to the mode where the pad dresser cants by the frictional force when the polishing pad performs high-speed motion and returns to the original attitude after that, as mentioned above. Although the dressing dispersion of the circumferential direction of the polishing pad mentioned above is caused by this phenomenon, the problem is not restricted only to this.
Also about the volume of the polishing pad swarf removed with the pad dressing, while the pad dresser does intermittent contact, the portion which can be cut off greatly, and the portion which can be cut off a little are intermingled, and dispersion in the volume of swarf becomes large. Since the polishing pad will be cut off with being exfoliated greatly as a result without the polishing pad surface being cut off finely and stably, the amount of the abrasion wear of the polishing pad abraded out by the pad dressing becomes large. As a result, the life of the polishing pad became short and the problem that the exchange cycle of the polishing pad is brought forward has also arisen. From such mentioned above, the traditional pad dresser holds the essential structural problems from the viewpoint of the surface reference grinding of an elastic body.
Further, in the traditional surface reference dressing mechanism, since the mechanism will perform dressing so that the surface of the polishing pad may be followed using a plurality of elastic members, the following various problems arise.
That is, in the case of mounting an abrasion-resistant material (for example, diamond abrasive grain) of high hardness to the tip part of the elastic member, the abrasion-resistant material (diamond abrasive grain) may drop with the friction at the time of the pad dressing. The technical difficulty of mounting the abrasion-resistant material with the sufficient accuracy to the tip part of the elastic member of the fine wire size is high, and the cost of the polishing device will become high as a result.
Further, in the case of using metallic materials etc. without using the abrasion-resistant material for the tip part of the elastic member, there arises such problem as the tip part has been immediately worn out, and the replacement frequency of the pad dresser will become fast extremely.
As elastic material of the pad dresser, a preferred material which has sufficient abrasion resistance with having proper elasticity against the dressing is required in order to follow the ups and downs of the surface of the polishing pad, and at present, such preferred material has not ever existed.
When the tip part of the elastic member is abraded out, the pad dressing capability abruptly decreases, and there is a possibility of causing remarkable lowering of the removal rate. As the result, when compared with the diamond dresser of a traditional disk type, there exists such problem as the elastic material cannot bear usage because the dresser replacement frequency thereof is high.
Accordingly, in order to enable it to use without replacing during a long period of time while having the proper elasticity for performing the dressing on the reference of the surface of the polishing pad, the technical subjects to be solved will come to arise, and the present invention makes it the object to provide the pad dresser and the polishing device that solve the subjects.